Tap changer



W; R. F ARLEY 'June 1o, 1930.

TAP CHANGER Filed Jan. 5,L 1929 2 sheets-sheet 1 Fig. .7.

3 INVENTOR William R Farley.

AT'TORNEY s Q5 s.

June 1o, 1930. w. R. FARLE'Y 1;v63,143

TAP CHANGER 'Filed Jan. 5, 1929 2 sheets-sheet 2 INVENTOR f Wil/iam R'arley.

AT'TORNEY NITED STATES PATENT' ol-'rIcE 1 WILLIAM n. Imaam,l o1 wIL1II NsI..unef PENNsYLvANIA,v lsfsIcNOal To wEsTINog HOUSE ELEOTPIO' a MANUFACTURING COMPANY, ,A CORPORATION OP PENNsYI.-

' vANIA w TAP CHANGE `Application mea January 5,1929; seria; N. sso,4s1.

My invention relates'gdnerally to transformer-tap-changing systems and particularly to automatic controlv of such systems.

The' practice of interconnecting large 5 ower systems necessitates the use of transormers equipped with tap-changing mecha-l nism which functions to vary the ratio of transformation between the interconnecting transformer systems, as desired. Such oints of interconnection are frequently so ocated that automatic control of the tapchanging system is desirable.' c My inventionprovides forautomatically vcontrolling theoperation of `a tap-changer mechanism for a transformer interconnecting two power systems, and the particular` embodiment to be described hereinafter is adapted to maintain the ratio of the number of effective turns in the primary and secondformer `substantially equal .toI the -ratio between the voltages of the systems, that is, to maintain a condition in which there is substantially no wattless power interchanged between the two interconnected systems. I have' provided a plurality "of relays for controlling the operationl of a motor which actuates the\tapchanging mechanism, and these relays are energized by voltages proportional to the voltage which each separate power system would have if it were not connected through the transformerto the other system. The relays are sodisposed and connected that, whenethe voltage of one system El is higherwthanthat of the other, the tap.

changer mechanism will be operated in `the properdirectionto bring about a ratio of transformation which will permit no wattless power interchange.

The extent of operation ofthe transformer is governed by a plurality of relays, the operation -of which will be described hereinafter.

The object of my invention, stated, .is to provide an automatic tapchanging system for a transformer which interconnects two power lines.

A further object of my invention is to provide a tap-changing's' stem which shall be automatically operate to so vary the ratio l generally of transformationasifo prevent'or limitthe cflov1 of wattless current between the power lines. u

In achievingthe purpose of m invention,

I yprovide means fol varying t e ratio fof transformation in a transformer connectedl between two power lines, in accordance with the compensated voltages of the' respective power lines so that the operation of the tap changer for the transformer shall be con- 0 trollecl in accordance with theldilerence between the voltages which the power lines would have, if not interconnected.

A still further object of my vinvention is' to provide means for controlhng the extent of the operation of a tap changer forv an interconnecting transformer whena difference in voltage occurs and in vaccordance with f v 'the magnitudes of the voltages. ary windings ofthe interconnecting trans- My invention l reference to the accompanying drawing in 'which-Fig. 1 illustrates apparatus and cir# cuits organized in accordance with myinvenf tion,andf` Fig. 2 illustrates a simpliged wir- 75'- ing diagram of the same system. Referring to the drawing, two 'power lines 10 andll are connected together through a transformer 12.v In this particular embodiment, the voltages of the two power lines are will-be better understood by ci variable throughout a considerable range,

the maximum and minimum yvoltages of the power line lObeing greater than the corresponding maximum and minimum voltages ofthe power line 11. The maximum voltage ofthe power lline 11 is, however, greater lthan the I'ninimumy voltage of the power line y i former 12Vsubstantially`equal Ato the ratiol between, the voltages of the power vlines 10 g5 land 11, a plurality of voltage v'taps 13 to 19,

inclusive, are provided on one vwinding of the transformer 12, and a movable contact arm 20 is providedto vary the number of effective turns in that winding by changingv mounted on the pivot 21 ,and is rotatable thereabout, it being actuated by the gear .segment 22 and an engaging worm gear 23 driven from a shaft 24 through a train of gears 25 and 26 which transmit power fromthe tapchanger driving motor 27. An induction regulator 28 is provided for use with the tap-changing systems to produce a smooth variation of voltage between values corresponding to those of adjacent trans-` former taps, and to insure a minimum amount of arcing between operating contact members. The action of such an induction regulator is thoroughly understood by those skilled in the art, and is operated simultaneously with the operation of the tap-changer system, since it is directly connected to the tap-changer operating motor-27 through a train of gears 29.

Upon one end of the shaft 24 is mounted 30 a second worm gear 30 which engages a gear segment 31, substantially like the segment 22, and, upon operation of the tap-changer loperating motor 27, a contact arm 32 is rotated about the point 33 to engage, succes- 35 sively, a plurality of taps 34 to46, inclusive,

.which lead from a reslstor 41, and, during the operation of the Contact arm 32, vary the portion of the resistor 41 that is connected in a relay circuit to prevent hunting of the system, as will be explained hereinafter.

The operation of the tap-changerwdriving motor-.27 in one direction functions to move the contact arm 20 in the direction of the transformer tap 13 and the contact arm 32 in the direction of the resistor tap 34, the

amount of movement of the Contact arm 20 corresponding exactly to the amount of movement of the contact arm 32.

When the direction of rotation of the motor 27 is reversed, the contact arms 20 and 32 are moved in a counter-clock-wise direction, that is, towards the taps 19 and 40, respectively. By controlling the direction and period of operation of the motor 27, it is,

therefore, possible to obtain the desired number of effective turns in one'winding of the transformer 12.

The motor 27 is operated by power supe0 plied from the three-phase supply line 42,

and the direction of its operation is controlled by the switches 43 and 44. The operation of the switches 43 and 44 is controlled by a circuit through one of the relays 45 and 46 and onepair of contact members of the voltage relays 47. The voltage relay 48 directly controlsthe relays 45 and 46. y

The switches 43 and 44 have their contact members so connected to th'e motor supply line that, when thefswitch 43is in. its circuitclosing position, the motor 27 operates in one direction, whereas, when the switch 44 is in its closed position, the motor 27 operates inl the reverse direction. The motor supply line may be traced lfrom the three-phase supply line 42 through conductors 49, the contact members of one ofthe switches 43 and 44 and, by conductors 50, to the motor 27.

The relays 47 and 48 are energized by voltages whichare proportional to the voltages of the power lines 10 and 11. These voltages are taken "from the secondary windings of the potential transformers`51 and 52 and are so compensated as to be proportional to the voltages which each of the power lines 10 and 11 would have if ,they were not connected together through the transformer 12. The compensators 53 and 54 compensate, respectively. for the voltage drop in the transmission lines 10 and 11, and, in ythis way, provide the compensated voltage'for energizing the relays 47 and 48. The operation of linedrop compensators, such as 53 and 54 is understood by those skilled in the art and it will be understood that any suitable compensating device may be used `for this purose.

The relay 47 is provided with a plurality of energizing coils 55, 56, 57 and 58, and it will be observed from the diagram that the energizing coils 55 and 58 are permanently and equally energized from the supply line 42 and that the coils act in opposition to each other. The coils 56 and 57 are disposed upon separate armatures, the actions of which oppose each other, and one of these coils will seldom be energized greatly in excess of the other, and. since it is well known to those skilled in the art that such relays, when operating under a lowvoltage, are less sensitive 'than when, operating under a higher voltage.with the same difference between opposing forces, the coils 55 and 58 are provided tb increase the energization of each of the armatures of the relay 47 and thereby to increase the sensitivity of the relay 47.

The coil 56 is energized by the voltage drops between the tap point 37 of the resistor 41 and the tap engaged by the movable arm 32. The resistor 41 is connected in shunt relation to the secondary winding of the transformer 51. Tha energization circuit for the coil 56 may be traced from the tap 35 of the resistor 41, through the contact arm 32. conductor 62, the ballast resistor 63, conductor 64, coil 56 and conductor 65. to the midpoint of the resistor 41 corresponding to the tap 37. It is apparent that, as the contactarm 32 is moved from one position to another, the energization of the coil 56 is increased or decrease vasv the amunt of resistance connected in arallel-circuit 'relation with it is increase or decreased. When the contact arm 32l is in engagement with the tap 37 of the resistor 41, the coil 56 is completely deenergized, and this, it will be remembered, corre- .n sponds to a position of the tap changer in which the ratio of turns between the primary and second windings of the transformer 12 is equal to the normal ratio between the voltages of the transmission lines and 11.

The coil 57 of the relay 47 isenergized by a voltage which is proportional to the difference between the voltages of the vpower lines l10 and 11. It will be apparent from therdiagram that the coil 57 is so connected that the voltages of the`potential transformers 51 and 52 oppose each other, and that the coil 57 is energized by the difference between the voltages supplied by the potential transformers '51 and 52. The energizing circuit for the coil 57 may be traced from the potential transformer 51 to the compensator 53, conductor 67, conductor 68, compensator 54, potential transformer 52, conductor 69, conductor 70, the ballast resistor 71, conductor 72, the coil 57 and, by conductor 59, to the potential transformer 51.

i If the contact arm 32 be assumed to be in engagement with the ta 37, so that the coilv 56 is not energized an the voltage on one of the power lines is disturbed by some outside source, so that a difference exists between j allow a shorter travel of the tap changer for fa given difference in voltage, as the contact arms 2O and 32 vof the tap-changer mechanisms move away from the middle taps 16 and 37, respectively. Itis obvious that a lesser change in effectivetrns in the transformer is necessary to obtaina balanced condition, as the voltage of either system departs farther and farther from its normal value. The coil 56 may, therefore, be understood as a limiting ,device which protects the mechanism from over-travel and de ends for its functioning upon the magnitu e of the voltage between the lconductors of the transmission line 10, as `wellas the voltage between the conductors of the transmission line 11 taken indirectly as the travel of the tap-changer mechanism.

The relay 48 is provided with two oppositely disposed energizing coils 73 and-74 which are energized, respectively, in accordance with the compensated voltage ,providedbyy the potential transformers 51 and 52. The relay 48 will, therefore, be actuated towards thek right when the voltage appligd to the coil 74 is greater than the voltage applied to the coil '(3,y and the relay 48 will be actuated to the left when the voltage a plied to the lcoil 73 is in excess of the Avo tage applied to the coil 74. The energizing circuit for the coil 74 may be traced from the potential `transformer 52 through conductor 69, the

ballast resistor 75, conductor 76, coil 74 and conductor 77 and, bf conductor 68, to the compensator`54 and t epotential transformer 52. The energizing circuity for the coil 73 may be traced from the 7p tential transformer 51 through conductor 59, conductor 60, ballast resistor 78, conductor 79, coil 73, conductor 80 and by-conductors 67 to the compensators 53 and the potential transformer 51. f l

The, relays 48 and 47, therefore, respectively control the direction and extent of the tap- /ohanger o eration in accordance with the difference etween the'voltages ofthe systems 10 and 11. The ballast resistors `63,. 1,

and 78 are provided to obtain adjustments of the system so that the relays will be actuated in accordance with desired voltage relations between the power lines.

If the yoltage of the power line I10 is decreased below its desired'value with respect to the voltage of the power line 11, it will be desired to move the tap-changer mechanism in a clockwise direction so that'the voltage per turn in both windings of the transformer will be maintained alike. When the voltage of the power line 1-1 is higher than its desired value, with respect to that of the power line 10,.tlie relay 48 will be actuatedgto lts right-hand position, bridging the Contact members 81, and an energizing circuitwill be thereby completed for operating the relay 46 to a circuit-closing position, and which may be traced from the middle conductor of the supply line 42, through conductor 82, con- 1oo l ductor 83, contact members 81, conductor 84,

theenergizing coil of therelay'46 and conductor 85, to the upper conductor of supply line 42. .It will be'recalled that the rela-ys U 45 and 46, together with the relay 47, control the energization of the switches'y 43 and 44,

and that, since the two pairs of Contact members of the relay 47 are each connected in series-circult relation with the contact mem` bers of the relays 45 and 46, no circuit will be completed to energize the switches 43 or 44 unless one of the coils 57 and 56 isenergized in excess of the other, so that the relay 47 is actuated to one of its circuit-closingyposi-v tlons.

If such a'dii'l'erence exists between the voltages of the potential transformers 51y and 52 that the coil 57 of the relay 47l is energized more than the coil 56, the relay 47 will be actuated to the right and bridge the contact v members 86. If, at the same time, the energization of the coil 74 of the relay 48 is greater than that ofthe coil 73, thus actuatingthis relay,a-circuit will be completed to the right to bridge the contact members 8.1, to

vcause energlzation of the operatingcoil of theV 88 of the relay 46 and conductor 89, to the operating coil of the switch 44 and thence to the upper conductor of the supply line 42. Such energization of theoperating coil of the switch 44 actuates its armature upwardly to complete a circuit for operating the motor 27 to move the contact arm 2O in a clockwise direction, thereby increasing the number of turns in the transformer winding to which the power line 11 is connected. When the tap changer has travelled far enough to move the contact arm 32 to a position in which the voltage impressed upon the coil 56 is sufficiently great to overcome the force exerted by the energization of the coil 57, the armature of the relay 47 will be moved to its neutral position, interrupting the energizing circuit for the switch 44 and thereby disconnecting the motor 27 from the supply line 42.

If the voltage of the power line 10 increases but still remains at a lesser value than its desired relation with respect tothe power line 11 tuated towards the left to bridge the contact members 90 and complete an energizingcircuit for the switch 43 and so connect the motor 27 to the supply line 42 that its direction of rotation will be reversed from its previous ydirection, thus causing the contact arms 20 andv 32 to be moved in a counter-cloclr-wise direction, whereby the voltage per turn in the windings of the transformer 12 is again brought to a uniform value, anda balanced condition is obtained in the relay 47 so that the tap-changer contact arm 20 stands in Vthe proper position to maintain equal voltages per turn in each of the windings of the transformer.

When the armature of the relay 47 is moved towards the left to bridge thecontact members 90, an energizing circuit is completed for the switch 43 which may be traced from the energized conductor 83 to contact members 90, conductor 91, contact member 92 of relay 46 and by conductor 93 to the operatting coil of the switch 43, thence returning to the supply line 42.

In the event that the voltage of the power line 10 is in excess of the voltage of the power line 11, the relay 48 will be actuated towards the left to bridge the contact members 94 and complete an energizing circuit for the relay 45 so that, when the armature of the relay 47 is in its righthand position, the switch 43 is operated to close the circuit to the motor 27, and, when the relay 47 is in its left-hand position, the contact members 90 are bridged to complete an energizing cirthe armatures of the relays 47 will be accuit for the switch 44 to reverse the direction of the motor 27, and it will be recalled that thisf scquency of switching is exactly the inverse of the case when the armature of the relay 48 was in its right-hand position, that is, when the voltage of the power line 11 was in excess of the voltage of the power line 10. The relation of the switches 45 and 46 may be understood when it is observed that the contact members 86v of relay 47 may be connected in series-circuit relation with either the contactl members 88 of switch 46 or the contact members 95 of switch 45, the first of which control the energization of switch 44 and the latter of which control theenergization of switch 43. Similarly, the contact members 90 of the relay 47 may be connected in series with either of the contact members 96 of the switch 45 or the contact members 92 of the switch 46, the first of which controls'y the energization of the switch 44 and the latter of which controls the energization of the switch 43.

My control system will, therefore, be understood to automaticall operate the tap changer in the proper irection when the voltage of one line is higher than the voltage of the other line and to automatically maintain similar voltages per turn in the primary andsecondary windings of the transformer 12 regardless of which power line has the higher voltage.

Since `the embodiment hereinbefore set Lforth may be modified in various ways and adapted to many systems without departing from the spirit and scope of my invention, it is desired that the foregoing description be construed as entirely illustrative and not in a limiting sense.

I claim as my invention:

1. An automatic tap-changing system for transformers comprising, in combination, a plurality of power lines, a transformer connecting said power lines, said transformer being provided with motor-operated tapehanging equipment, and means for controlling the motors to operate the tap-changing equipments for maintaining the ratio of cordance with changes in the position of the v tap changer.

3. In a tap-changing system for a transformer, means for operating the tap changer, means for automatically controlling said operating means in accordance with the difference between the voltages on opposite sides of the transformer and means for compensating said last named means in accordance with the power flow through the transformer.

4. In combination, a. transformer, a plurality of power lines connected to said transformer, a tap changer for varying the rat-io of transformation in said transformer, a. motor for operating said tap changer, and means for automatically controlling said motor to operate the tap changer and maintain the ratio of effective turns equal to the ratio of voltages impressed on opposite sides of the transformer.

5. In combination with a transformer having primary and secondary windings connected -to different power lines, a tap changer formaintaining the voltages per turn in said transformer windings at a constant ratio, a motor for operatmg said tap changer and a plurality of relays for controlling said motor,-

one of said relays having two windings energized, respectively, in accordance with voltages proportional to the.' voltages of the respective power lines,vthc other of said relays having two windings energized, re' spectivelyin accordance with the difference in the voltages of the two ower lines and in accordance with the position of the tap phanger and the voltage of one of the power mes. l

6. In ycombination with a transformer having primary and secondary windings for interconnecting power lines, a tap changer for maintaining the voltage per turn in said transformer windings constant, a motor for operating said tap changer, and a plurality of relays for controlling said motor, one of said relays being energized by voltages proportional to the normal voltages of the re-y spective power line and automatically actuated to operate the tap changer in one direction when the voltage of one line is higher than its desired relation to the other line and for reversing said operation when the voltage of the other line is higher, another of said relays disposed to be actuated in. accordance with the difference between said proportional voltages, the operation of said latter relay being restricted in accordance with the magnitude of the line voltage of one power line and the travel of the tap changer.

7. In combination, a plurality of power lines;y a transformer interconnecting said power lines 'and having primary and second' ary windings, a motor-operated tap changer for said transformer, an automatic control s stem for said motor, whereby the tap hanger is operated tor maintain equal voltages per turn in the windings of the transformer, said operation being controlled by a relay energized in accordance with the difference between the line voltages and compensated in accordance with the travel of the tap changer. Y

8. In combination with a plurality of power lines, a transformer connecting said power lines, said transformer being provided with a tap changer and means for automatically operating said tap changer in accordance with the difference between the voltages of the power lines, and means for limiting said operation, said means being re- `sponsive to the relation between said volt age differences and the magnitude of the voltage of one power line.

9. In combination, a transformer connected between two power lines and having primary and secondary. windings, a tapchanging system for the transformer, means for automatically varying the ratio of transformation to maintain equal voltages per turn in the transformer windings, said means comprising a motor-operated tap changer and [a control system therefor including a relayhaving one coil energized in accordance with the difference between the voltages of the power lines and a second coil opposing said first coil, and a. variable resistor operated by said tap changer, said second relay coil being connected in circuit with said variable resistor whereby said second relay coil is energized in accordance with the travel of the tap changer.

In testimony whereof, I have hereunto subscribed niy name this 11th day of December,

WILLIAM R. FARLEY. 

